Hi, thanks for your support!
No, I’ve never used pokeemerald-expansion, but I can look into it and get back to you.
Generally speaking, you’ll want to make sure your sprite sheet layout and frame dimensions (both configurable on the Configuration screen in TDSM) match the layout and dimensions of the sprite sheets you are replacing.
As of v1.2.0, TDSM only exports sprite sheet PNG images with 32-bit RGBA colors. ROM hacks typically expect 4BPP (4 bits per pixel) images with accompanying palette data provided by a separate file.
My recommendation to you would be to take your exported sprite sheets from TDSM and convert them using a tool like Porypal, which is free and open source. Porypal is designed for Gen III ROM hacking sprite compatibility, and lets you convert your standard 32-bit RGBA PNGs to 4BPP PNGs that should work perfectly in a hex editor or with pokeemerald-expansion (don’t quote me on that just yet though!).
Let me know if that makes sense :)